The invention relates to a device for aligning material webs.
Such devices are used whenever material webs are required to be precisely positioned and aligned for a subsequent processing stage, generally cutting into individual pieces of material.
Material webs of the type presently under discussion have regions of differing thickness alternating in a longitudinal direction. For instance, in the case of terry toweling material, there are usually pile-free sections provided at regular intervals and extending at right angles to the longitudinal direction of the web, the distance between said pile-free sections corresponding substantially to the length of the finished product to be produced, e.g. a hand towel. Since cutting of the continuous material web is effected in the region of said pile-free sections, the material web while being conveyed has to be positioned and aligned by a suitable installation in such a way that, on the one hand, the pile-free section is precisely positioned in relation to a cutting or separating device and, on the other hand, the material web at least in said region is aligned in such a way that distortions involving a curvilinear and/or oblique-angled course of the woven, in particular of the weft yarns and the pile-free sections, are reliably avoided at least in said region.
From German patent specification DE 25 44 410 C3, a device for aligning and cutting material webs of differing thickness in a longitudinal direction is known, which comprises a top aligning rail having a row of aligning elements, which are disposed alongside one another substantially over the entire width of the material web and may be brought to rest on a table acting as an abutment, the material web which is to be aligned lying between the aligning elements and the table. Said aligning elements are supported in the top aligning rail so as to be movable under the action of a spring in a direction at right angles to the material web. At their bottom end directed towards the material web, the aligning elements have a wedge-shaped shoe which is pressed by the resilient restoring force of the spring onto the material web in the region of the pile-free sections. Because of the tensile forces exerted by a conveying device upon the material web, the material web in the case of the known device is pulled relative to the aligning device until the start of the raised pile region "pushes against" the edge of the shoes of the aligning elements. Since the tensile forces are exerted uniformly over the entire width of the material web, the result is that, over the entire width of the material web, the start of the raised pile region comes to rest against the aligning elements forming the aligning rail, thereby enabling a precise alignment of the material web in said region.
The main drawback of said known device is that, because of the flexible, spring-loaded mounting of the aligning elements, even with relatively low tensile forces upon the material web it is impossible reliably to prevent a lifting of the aligning elements caused by the raised pile region moving under the shoes of the aligning elements. This then leads to the pile region slipping through the aligning device; reliable positioning is no longer possible. A further drawback of said known device is that, especially if the material web has regions of differing thickness also in transverse direction, e.g. edge regions with no pile, hem regions etc., the contact pressure of the individual aligning elements is not uniform over the entire width of the material web. Because of the non-uniform retaining forces caused thereby, an undesirable slipping through of portions of the material web under the aligning device cannot be reliably ruled out.